Hydraulic press



Jan. 9,1962 J. w. TOMKA ET AL 3,016,005

HYDRAULIC PRESS Filed Jan. 5, 1956 2 Sheets-Sheet 1 I IN V EN T025. 05%2/5 9/." (713223 .Irz v/ zl 200k Jan. 9, 1962 J. w. TOMKA ETAL HYDRAULIC PRESS 2 Sheets-Sheet 2 Filed Jan. 5. 1956 flwl RHHRM O 5? Ban (VARIABLE) United States Patent 1 3,016,005 HYDRAULIC PRESS Joseph W. Tomka and Robert C. Brenk, Cincinnati,

Ohio, assignors, by mesne assignments, to Elmes &

King Manuiactm'ing Company, Cincinnati, Ohio, a copartnership Filed Jan. 5, 1956, Ser. No. 557,491) 12 Claims. (31. 100-43) This invention relates to hydraulic presses and more particularly to a novel hydraulic control circuit adapted to control the power stroke of the press slide.

There are certain instances when it is desirable to use a mechanical press type of motion during the power stroke of the slide of a hydraulic press and at the same time to retain the inherent advantages of a hydraulic press. The slide of a mechanical press generally is driven by means of a crank which imparts to the slide sine curve motion. Deceleration or" the slide from maximum speed to Zero on a sine curve is sometimes desirable. However a mechanical press is generally limited to the same type of motion during the portion of the advance stroke prior to the working stroke, and also on the entire return stroke of the slide. It would be desirable, therefore, to incorporate sine curve deceleration in the working stroke of the slide of a hydraulic press because a rapid advance stroke and a rapid return stroke could also be maintained.

It is a primary object of this invention to provide a control system for a hydraulic press which will enable the press to be operated in a manner simulating mechanical press action during the working portion of the stroke.

Another object of the invention is to provide a hydraulic press control system which will impart to the press the advantageous characteristics of a mechanical press during the power stroke, but will not adversely affect normal hydraulic press action during other portions of the stroke.

Another object of the invention is to provide a control system for a hydraulic press whereby the press slide may be decelerated, during its power stroke, from a preselected maximum speed to zero speed along a predetermined deceleration curve.

Other objects will be apparent from the following specification, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a front elevational view of a hydraulic press with which the present invention may be utilized, the press being shown only schematically in order to better show the basic working parts;

FIGURE 2 is a diagram of the novel hydraulic circuit;

FiGURE 3 is an enlarged view of the power stroke control mechanism; and

FIGURE 4 is an enlarged view of the control cam.

The invention can probably best be described in conjunction with a description of an operating cycle of the press. FIGURE 1 illustrates a typical hydraulic press comprising a bed on which is mounted a pair of pushback, or return cylinders, 12, which carry for reciprocating motion therein push-back rams 14. It should be noted that the hydraulic press herein described is by way of illustration only and the inventor does not intend his invention to be limited to this press. It will be apparent that the invention may be adapted to any type of hydraulic press having ram means with advance and return areas in advance and return chambers which may be incorporated in one cylinder or in separate cylinders as desired. Mounted at the upper ends of the push-back rams is a press slide 16, which, in turn, carries a tool such as a punch 18. A portion of the frame 20, constituting a main ram cylinder, is supported by columns 21 which are secured to the bed. The columns 21, in addition to supporting the main ram cylinder 20, also comprise guide surfaces to accommodate reciprocal vertical movement of the slide 16. The main ram 22 is secured at its lower end to the slide 16 and extends upwardly into the cylinder 20 (see FIGURE 2). A suitable hydraulic packing 24 is used at the lower end of cylinder 20. A conventional ejection mechanism 19 is provided, by means of which a completed work piece may be ejected from a die (not shown) which is mounted on the press bed beneath the slide.

Referring to FIGURE 2, it should be noted that the main high pressure lines are shown solid and are connected to the press cylinders and also to a conventional source (not shown) of high pressure fluid such as a pump and accumulator system. The various hydraulic control elements, which will be described hereinafter, are operated by low pilot pressure. The pilot lines, which convey the low pressure fluid, are shown dotted, and are connected to a conventional source of low pressure fluid (not shown). Also provided is a conventional surge valve 25, which is connected to the main cylinder, and which accommodates flow of fluid from behind the main ram on the upward stroke of the ram and slide, and which also supplies the necessary fluid from the reservoir to fill the void in back of the main ram on the downward rapid advance stroke of the ram and slide. The surge valve also is conventional and is shown only schematically inasmuch as it forms no part of the present invention. For purposes of illustration a single action type press has been shown, but it will be obvious to those skilled in the art that this invention could readily be used on a multiple action type ram wherein both high and low press tonnage would be available.

We may assume that, at the start of a press cycle, the slide would be at the top of the stroke in extreme upward idle position and the mass of the slide and ram would be held up by hydraulic fluid whichis trapped under the push-back rams at this portion of the cycle, as will be hereinafter described.

To initiate the press cycle the operator would press a button (not shown) causing solenoid operated valves 26 and 28 to be energized to shift the valve spindles downward. At this time, hydraulic fluid such as oil will be free to flow, under pilot pressure, from port 30 to port 32, and from port 34 to port 36 in valve 26, and also from port 38 to port 40 and from port 42 to port 44 in valve 28. Pilot pressure fluid, therefore, flows through lines 46 and 48 into the lower side of spindles 5t and 52 of a three-way valve 54, causing them to be shifted upwardly. At the same time fluid will be exhausted from above the spindles 50 and 52 and pass through return lines 55, through valves 26 and 28, and through lines 64 into the reservoir '62. With the spindles of valve 54. shifted to the upward position fluid will be free to flow from the push-back cylinders 12, through ports 56, line 58, through the ports of spindle 50, and into the reservoir 62, whereupon the push-back rams 14, together with the slide, will be free to move downward in free-fall. The rate of freefall of the slide may be controlled by means of a slide advance speed control valve 60, inserted in the line between the spindle 50 and the reservoir 62.

At this time there will be no flow or" fluid through the open ports 63 and 65 of spindle 52 inasmuch as a relief valve 66 is inserted in the line between the spindle 52 and the reservoir 62. The purpose of this relief valve will be explained hereinafter. While the slide is falling, a port 68 on the main cylinder is open to accommodate flow of fluid from the reservoir through the surge valve 25 to fill the void created in the cylinder 23 as the ram 22 moves downward. The action of the surge valve is conventional, and therefore need not be explained in detail.

The slide falls on rapid advance stroke until a cam 79, mounted on the slide, strikes a slowdown limit switch 72. Tripping the switch 72 deenergizes solenoid operated valve 26. Pilot pressure fluid now flows'through ports 30 and 34, though line 55 and to the topof spindle t causing the spindle to move down to the closed position. The fluid from the push-back cylinder is still free to flow through the ports of spindle 52 and begins to build up pressure against the spring of relief valve 66. It should be noted that the slide cannot, of its own weight, overcome the resistance of relief valve 66, so momentarily the slide will tend to slow down, but the slide will not come to a complete stop due to other action which is taking place in the hydraulic circuit.

Tripping limit switch 72 also causes the surge valve 25 to close thereby shutting ad free flow of fluid from the reservoir to the main cylinder. Tripping limit switch 72 also energizes solenoid'pilot operated valve 74 causing the valve spindle to shift downwardly to the open position to accommodate pilot fluid flow from port 76 to 78, through line 80, and to the lower side of the shifting cylinder 82 of the main operating valve 84. At this time the fluid from the top of shifting cylinder 82 is exhausted through line 86 and through a solenoid operated pilot valve 83 to the reservoir, valve 88 at this time not being energized. As the piston of the shifting cylinder 82 moves upward it lifts the long arm 90 of rocker arm 92 which contactsand moves the spindle 96 of the main operating valve 84 upward to open position. This action permits the flow ofhigh pressure fluid from its source through line 98, through the ports of spindle 96, through the line 160- and through a throttle valve 102, through line 196 and through port 108 into the main cylinder 20, causing the ram slide to move downward through the power stroke of the press. Associated with the throttle valve 102, however, is a power stroke control mechanism, indicated generally at 164, by means or" which the power stroke of the press may be made to simulate mechanical press action. it should be noted here that it may be desirable to insert in the line a pressure compensating valve 111'), which must be upstream from the throttle valve 102 so that full tonnage may be developed'at all times. The pressure compensating valve is conventional in the art and therefore need not be described in detail. 7

The power stroke control mechanism 104, which is shown only schematically in FIGURE 2, is shown in greater detail in FIGURE 3, and comprises a cam 112 which is secured to the press slide for movement therewith, the cam being operatively engageable with one end of a rocker arm 114 which'is pivoted approximately centrally thereof to the frame of the press and is provided at each end with cam followers 116; The other end of the rocker arm 114 is operatively engageable with a push rod 118'slidably received within a sleeve bearing 120 which is secured to the pressframe; The push rod 118 is, in turn, engageable with a valve control rod 122 which controls the port openings in the throttle valve 102. The push rod and valve control rod may be provided with hardened faces 124 to minimize the wear on these parts. Also provided is an adjusting screw 126 which is supported at one end by a sleeve bearing 128, and which is provided with a hardened end 130 operatiyelyrengageable with the cam follower 116. The adjusting screw is received within and supported at its distal end by a stationary nut 132. It is preferable to provide also a wrench 134 to facilitate rotation of the screw 126, a lock nut 136 to maintain the screw in its adjusted position and a pointer 138 whereby V the position of the adjustment screw may be determined from the relationship between the pointer 138 and indicator markings 149 provided on the screw.

Returning once more to the operation of the control mechanism the rate of fall of the slide at the beginning of the power stroke is determined by the particular setting of the valve 102 by means of adjustment screw 126. In

the extended control rod position full oil flow is permitted through valve m2. In the particular press in which this device has been incorporated, the slide speed at this time will be approximately 600 inches per minute. As the slide moves downward the curved portion 142 of the cam 112 contacts the rocker arm 114 causing it to pivot and move control rod 122 inward relative to valve 192, thereby gradually cutting ofl the flow of fluid through the control valve 102 until the shutoff point is reached and the slide movement is completely stopped. The deceleration of the slide from its maximum speed to complete stop will be controlled by the shape of the cam surface 142 which preferably is in the form of a sine curve and therefore representative of the harmonic speed curve of a mechanical press slide. However, it will be obvious to thoseskilled in the art that any type of controlled deceleration may be obtained merely by substituting cams having the desired contour.

Referring for a moment to FIGURE 4, which illustrates the stroke control cam 112, it is apparent that the length of the power stroke may be varied as desired merely by varying the length of the cam rise 142. The distance from the maximum speed line 144 to zero speed line 146, representing the amount of deceleration during the power stroke, may also be varied as desired. It is also possible, without changing the cam, to decelerate the press slide from a maximum speed of less than 600 inches per min ute down to zero. This is accomplished by moving the adjusting screw inward toward the valve 1432, thereby pivoting the rocker arm 114 so that the end of the arm, which is normally engageable with the maximum speed line of the cam, is moved away from the maximum speed line to any predeterined point such as represented by line 148 in FIGURE 4. Moving the adjusting screw in this manner also moves the control rod 122 to partially constrict the flow through valve 102, thereby permitting the slide to decelerate rapidly to, for example, 300 inches per minute, at which time the rocker arm will contact the cam, and deceleration of the slide through the power stroke will occur along the desired curve from a speed of 300 inches per minute to zero. It should be noted again at this point that, as described hereinbefore, rapid deceleration of the slide from its free-fall speed is controlled by the three-way valve 54 and the terminal speed of free fall, which corresponds also to the initial speed at the power stroke, will be determined solely by the amount of high pressure fluid which is permitted to pass through the control valve 102 and thence to the main cylinder 20 to urge the ram and slide downward. If mechanical press action is not desired, normal hydraulic press action may be obtained by removing cam 112 from the press slide. The maximum desiredpressing speed is obtained once more by metering flow through valve 132 by means of adjusting screw 126, as described above.

The end of the stroke is controlled by means of a limit.

switch 150 and a pressure switch 152. The pressure switch 152 has two contacts which close at a predetermined value of rising or falling pressure. For example, when the cam 70 trips limit switch 150, the solenoid operated valve 74 is deenergized and the solenoid operated valve 28 is also deenergized, and a bleeder valve 154 in the line from the surge valve 25 to the reservoir 62 is energized. Energizing bleeder valve 154 permits a slow pressure bleed off from the main cylinder 20 through the surge valve, through the bleeder valve 154, and to the reservoir, thus allowing a gradual drop of pressure in the main cylinder and preventing heavy hydraulic shock on the press, which would occur if the main cylinder pressure were released too rapidly. When the pressure has dropped to the low pressure setting of the pressure switch 152, the surge valve is opened completely in a conventional manner, and the hydraulic'fluid in the main cylinder is free to flow unimpeded to the reservoir.

When valve 74 is deenergized pilot pressure fluid is blocked from the lower side of shifting cylinder 82 and communication is afforded from the lower side of cylinder 82 through valve 74 to the reservoir. This permits the spring 95 of spindle 96 of the main operating valve 84 to move the spindle to a neutral position thereby cutting ofl the supply of high pressure fluid to the main cylinder. The contacting of the low pressure setting of the pressure switch 152 also energizes the solenoid operated pilot pressure valve 88. Energizing this valve moves the spindle downward and permits pilot pressure fluid to flow from valve 88 through line 86 to the top chamber of the control cylinder 82, thereby causing the piston of cylinder 82 to move downward beyond the neutral position. This action pivots rocker arm 92, and the short arm 94 thereof raises the spindle 156 of the main operating valve 84. This action permits flow of high pressure fluid through line 98, the ports of spindle 156, line 158 and line 58 into the push-back cylinders 12, causing the slide to move upwardly and away from the work piece at a constant rate of speed. The deenergization of solenoid operated valve 28 permits flow of pilot pressure fluid to the top of cylinder 52 and the exhaust of fluid from the lower portion of the spindle thereby moving the spindle downward and preventing flow of high pressure fluid through valve 52 and into the reservoir.

The slide moves upward until the'cam 70 on the slide contacts limit switch 160, causing solenoid operated valve 88 to be deenergized, thereby blocking flow of pilot pressure fluid to the top of cylinder 82, permitting the spring of spindle 156 of valve 84 to return to the neutral or shutoii position. This action stops all flow of pressure fluid to the press circuit and the ram will stop and be retained at the top of the stroke, ready to start another cycle.

It should be noted that on slide reversal duplication of mechanical press action is not accomplished. On the contrary, the slide returns at a constant preset rate of travel, whereas on a mechanical press the upward stroke is a mere reversal of the downward power stroke.

The above operational description clearly illustrates that a control system has been provided for an hydraulic press by means of which a rapid advance stroke of the press slide may be obtained along with a rapid, constant speed return stroke. However, deceleration during the power stroke may simulate the harmonic motion of a mechanical press slide or, alternately, may follow any desired deceleration curve by the simple expedient of substituting a cam having a rise of the desired contour.

We claim:

1. In a hydraulic press, the combination of a frame having a bed adapted to support a work piece carrying die, advance and return chambers and ram means reciprocable therein toward and away from the bed, a source of high pressure fluid, a main operating valve adapted to selectively direct high pressure fluid to respective chambers, and means to control the stroke of the slide comprising a three-way valve adapted when in a first position to exhaust fluid from said return chamber and thereby permit free fall of said ram, a first throttle valve associated with said three-way valve to control the free-fall speed of the ram, a second throttle valve interposed between said main operating valve and the advance chamber and adapted to vary the speed of the ram proportionately to the rate of flow through said second throttle valve, said second throttle valve having a piston rod extending outwardly thereof, cam carried by the ram for movement therewith, a rocker arm secured to the press, one end of said arm being operatively engageable with said piston rod and the other end of said arm being engageable with said cam, whereby rocking of said arm by said cam operates to move said rod to vary the rate of flow of hydraulic fluid through said second valve to said advance chamber.

2. In a hydraulic press, the combination of a frame having a bed adapted to support a work piece carrying die, advance and return chambers and ram means reciprocato exhaust fluid from the return chamber and thereby permit free fall of the ram, a first throttle valve associated with said three-way valve to control the free-fall speed of the ram, a second throttlevalve interposed between the main operating valve and the advance chamber and adapted to vary the speed of the ram proportionally to the rate of flow through said second valve, and cam operated means adapted to vary the rate of fluid flow through said throttle valve to said advance chamber.

3. A device according to claim 2, wherein said cam operated means is responsive to movement of the ram during its downward stroke.

4. In a hydraulic press, the combination of a frame having a bed, a slide carried by said frame and movable vertically toward and away from the bed, ram means movable with said slide and having advance and return chambers associated therewith, a source of high pressure fluid, a main operating valve adapted to selectively direct high pressure fluid to the advance or return chambers, high pressure fluid lines affording communication between said valve and respective chambers, and means to cause said slide to simulate mechanical press motion during its power stroke, said motion consisting of deceleration on a sine curve from maximum. speed to zero, said means comprising a throttle valve interposed in the line from said operating valve to said advance chamber, said throttle valve being adapted to vary the fluid flow to said advance chamber and thereby vary the speed of said slide in proportion to the amount of opening of said throttle valve, and speed control means to permit free fluid flow through said throttle valve for a predetermined portion of the slide stroke and gradually diminishing flow for the remainder of the stroke, said control means comprising a valve stem projecting externally of said throttle valve, a rocker arm pivotally mounted on said frame, one end of said arm being operatively associated with said stem whereby pivotal motion of said arm will impart linear motion to said stem, and the cam secured to said slide for movement therewith, said cam having a rise portion in the form of a sine curve, said rise portion being operatively engageable with the other end of said rock arm.

5. In a hydraulic press comprising a bed, advance and return chambers, and ram means reciprocable therein toward and away from said bed; a control system to control the movement of said ram comprising a source of high pressure fluid, a source of pilot pressure fluid, pilot operated means to exhaust fluid from said return chamber during the downward stroke of the slide, other pilot operated means to direct high pressure fluid to the advance chamber, and means responsive to the position of said slide on its downward stroke to reduce the speed of the slide from the predetermined maximum speed at the beginning of the power stroke to zero speed at the end of the power stroke, said last-mentioned means comprising a throttle valve interposed between the high pressure source and the advance chamber, said throttle valve being adapted to variably regulate the amount of fluid flow to the advance chamber, and valve control means to regulate in a predetermined manner the rate of fluid flow through said throttle valve.

6. A control system according to claim 5, wherein said valve control means comprises a rocker arm operatively associated with said throttle valve to close the latter when the arm is moved from a first to a second position, and a cam mounted on the ram, said cam having a rise surface operatively engageable with said rocker arm as the ram moves downward whereby said arm will be moved from said first to said second position.

7; A control system according to claim 6, wherein the rise of said cam is in the form of a harmonic motion said means being adapted to independently pivot said arm from its first to its second position, thereby decreasing the initial speed of the controlled portion of the press stroke. 7 i

9. In an hydraulic circuit for an hydraulic press having advance and return chambers and a ram with advance and return areas in respective chambers, said ram having a power stroke of controlled length and controlled dcceleration, the combination of: operating valve means for delivering pressure fluid to each of said chambers While exhausting the other; throttle valve means in the connection between said operating valve means and the advance chamber; and control means for adjusting said throttle valve means to regulate flow of pressure fluid therethrough, said control means comprising a plunger operatively connected to the throttle valve means, a rocker arm operatively engageable with said plunger for moving said plunger from an open first position to a closed second position, a cam carried by said ram and engageable with said rocker arm to actuate the latter, and adjustment means operatively engageable with said rockerarm and said plunger to vary the length of the power stroke by adjustably varying said first position, said adjustment means comprising an axially movable rod, said rod being adapted, upon said axial movement, to shift said plunger and rocker arm to thereby change the initial point of en-. gagement of said cam with said rocker arm.

10. In a hydraulic press comprising a bed, advance and return chambers, and ram means reciprocable therein toward and away from said bed; a control system to control the movement of said ram comprising a source of high pressure fluid, a source of pilot pressure fluid, pilot operated means to exhaust fluid from said return chamber during the downward stroke of the slide, other pilot operated means to direct high pressure fluid to the advance chamber, and means responsive to the position of said slide on its downward stroke to reduce the speed of the slide from the predetermined maximum speed at the beginning of the power stroke to zero speed at the end of the power stroke, said last-mentioned means comprising a throttle valve adapted to regulate the amount of fluid flow to the advance chamber, the downward speed of the ram being proportional to the rate of fluid flow to the 7 advance chamber, a cam mounted on the ram, a rocker arm, one end of said arm being operatively associated with said valve to close said valve when moved from a first to a second position, and the other end of said arm being operatively associated with said cam during a portion of the downward stroke of the ram, said cam being adapted to move said arm from said first to said second position, and adjustment means operatively associated with said arm to vary the first position thereof.

11. In a control system for a hydraulic press having a ram vertically reciprocal in a main cylinder and having a controlled deceleration power stroke; the combination of a source of high pressure fluid, a line interconnecting said source and said main cylinder; throttle valve means in said line operable to vary the rate of fluid flow to the main cylinder in proportion to the amount of opening of said valve, whereby the deceleration rate of the ram throughout its power stroke will be proportional to the rate of fluid flow into the main cylinder, and means responsive to the position of said ram to move said valve from an open to a closed position, the rate of closure of said valve being condition responsive to said means, said last mentioned means comprising a cam secured to said ram for movement therewith, said cam having a rise position formed to the desired power stroke deceleration curve of said ram, and a rocker arm secured to the press, one end of said arm being in operative engagement with said cam, the other end of said arm being in operative engagement with said valve.

12. In a control arrangement for imparting mechanical press-type motion to the powerstroke of a hydraulic press having a ram reciprocal in a main cylinder, the combination of: a source of high pressure fluid; a line connecting said source and said main cylinder; throttle valve means in said line operable to vary the rate of fluid flow to the main cylinder inproportion to the amount of opening of said valve, whereby the deceleration rate of the ram throughout its power stroke will be proportional to the rate of fluid flow into the main cylinder; and means responsive to the position of said ram to move said valve from open to closed position, said last mentioned means including a cam formed substantially to a sine curve contour.

References Cited in the file of this patent UNITED STATES PATENTS 

